A comparative study of ordinary and mineralised Portland cement clinker from two different production units Part II:: Characteristics of the calcium silicates

Portland cement clinkers from two production units were investigated in order to determine the effects of mineralisation on alite and belite; Plant 1: ordinary clinker (P1) and clinker mineralised with CaF2 + CaSO4 (P1M); Plant 2: ordinary clinker (P2) and two clinkers mineralised with CaF2 + CaSO4 (P2m, P2m'). The polymorphism of alite was studied using synchrotron X-ray powder diffraction (XRD), wavelength 1.5227 Angstrom, and electron diffraction (ED) in a transmission electron microscope. The substitutions of minor elements in alite and belite were determined using electron microprobe analysis. Clinkers P1 and P1m both contained apparent rhombohedral alite (XRD) with an incommensurately modulated structure (ED), while clinkers P2, P2m, and P2m' all contained monoclinic alite (XRD). The addition of mineralisers in the process caused increased content of fluoride in alite and increased substitution of Si(4+) by Al(3+) and S(6+) in both calcium silicates. The latter effect was most pronounced in clinker P1m due to its high molar SO3 to alkali oxide ratio (R = 2.18). The improved hydraulic activity of P1m compared to P1 was caused by substitutions rather than a change in symmetry. The decreased hydraulic activity of P2m and P2m' compared to P2 was explained by the high levels of fluorine, which had a retarding effect on the hydration. (C) 2003 Elsevier Ltd. All rights reserved.